Age-related dysfunction of the immune system (immunosenescence) is a hallmark of aging and a significant health risk for the elderly. Studies of humans and other vertebrates have identified many age-related changes in the cellular components and physiology of the immune system that contribute to reduced immune function. However, the underlying causes of these changes, including the genetic influences on immunosenescence, are poorly understood. This is a major gap in our knowledge and limits our ability to design age appropriate targeted therapy to address this important health risk. A promising and novel approach to this problem is to apply age-specific genome wide association mapping to identify genes that influence immunosenescence. The proposed project combines a genomic and functional genetics approach to identify genes that regulate the age-specific ability to clear infection. The first aim uses the Drosophila Genetic Reference Panel, a set of 205 fully sequenced lines of Drosophila derived from a natural population, to identify genes that influence the age- specific ability of Drosophila to clear bacterial infection by E. coli. The second aim will validate the effects of candidate genes on a key component of innate immunity, age-specific phagocytosis. Drosophila are ideal for this study for three primary reasons. First, the genes and signaling pathways regulating the innate immune response are highly conserved between insects and mammals, so our results will provide gene targets for follow-up studies in vertebrates. Second, genome-wide association studies in flies can be carried out on large numbers of replicated genotypes under environmentally controlled conditions for the entire life span of the organism, greatly enhancing our power to identify candidate genes. Third, extensive genetic resources for Drosophila allow follow-up functional genetic tests to validate the effects of genes/pathways on age- specific immunity. We expect to accomplish two goals: (1) use genome wide association tests to identify candidate genes influencing the age-specific ability to clear infection; (2) to characterize the role of Arl2 (human orthologue ARL2), for its effect on phagocytosis in young and old flies. The expression of this gene, and those involved in actin regulation and endosomal transport, were significantly associated with age-specific bacterial clearance ability in our earlier transcriptomic study. Our strategy for verifying the effects of Arl2 on immunity will be used on additional candidate genes identified in Aim 1 as time allows. The project is innovative in its focus on genes influencing age-specific immune function, with focus on different aspects of phagocytosis (engulfment and processing of ingested bacteria). The results will advance our understanding of the genetic basis of age-specific immune function and provide genetic targets for enhancement or restoration of immune function in the elderly.